When I opened up the HS-81's BTW, I found no evidence of any oily residue anywhere inside the case. And if you opened one yourself you would see that the route that oil would need to take kinda rules out oil getting in the pot. What I'm thinking is it's the vibration that is causing a poor contact in the feedback pot whether it is abrading one of the surfaces (more likely the resistive surface) and the resulting dust causing the problem or the spring tension on the wiper is decreased causing intermittent contact. I'm leaning toward the first explanation right now.

OR... I could be all wet,

JESTER